Rifles often can be fitted with two primary types of barrels: tapered or bull barrels (also known as target barrels or heavy barrels). The bull or target barrel typically has a non-tapered or cylindrical shape, whereas a tapered barrel (typically affixed to most firearms) is tapered toward the muzzle such that the diameter at the muzzle is less than a diameter at the receiver. The non-tapered nature of bull barrels means that they are steadier due to greater weight, less prone to vibration due to their geometry, and can absorb more thermal energy due to their greater mass of metal (and hence are less prone to warping under repeated firing), and are therefore preferred in some applications. Most firearm stocks are shaped to support either of these barrel types, but not both. This means that users who wish to switch barrel types must buy and install an entirely new stock when installing a new barrel. U.S. Pat. No. 8,056,278 provides one solution to this problem in the form of a stock that supports a bull barrel and an insert that can be fitted into the stock to support a tapered barrel. Thus, the '278 patent enables a change in barrel types without the purchase and installation of an entirely new barrel. However, this design suffers from the need to store and keep track of the insert when the stock is used with a bull barrel and hence without the insert.
One application where the switching of barrels occurs is the RUGER 10/22, a widespread .22 caliber rifle platform. The RUGER 10/22 includes a safety pin that is perpendicular to the barrel and arranged on the top front portion of the trigger guard just below the stock. When the trigger guard is inserted into the stock the safety pin must clear an opening in the bottom of the stock shaped to pass the trigger guard. However, the safety pin will impinge one or another side of this opening unless the safety pin is ‘centered’ in the trigger guard such that neither end of the safety pin extends beyond the sides of the trigger guard.